The long-term goal of this program of research is to understand mechanisms that contribute to immature listening during normal auditory development. The proposed work will investigate if the medial olivocochlear (MOC) reflex plays a significant role in selective listening for infants and adults. Previous work has shown that, in adults, MOC effects are altered by directed-attention and listening in noise. If the MOC is involved in selective listening, it is possible that development of cortical influences on the MOC response is related to how infants detect sounds in noise. This novel approach will be examined by measuring how infants separate sounds from background noise and whether immature MOC function contributes to infants'susceptibility to interference from competing sounds. A combination of psychophysical and physiological tests will be used in this study. MOC reflex activity will be determined by measuring transient evoked (TEOAE) and distortion-product (DPOAE) contralateral suppression. Infants and adults will also be tested in three masking conditions that place different demands on selective listening. Tone detection will be measured in 1) broadband noise (BBN) 2) a 4-component fixed-frequency masker and 3) a 4-component random-frequency masker. The relationship between MOC reflex strength and masked thresholds will be determined. The proposed research will help identify mechanisms important for selective listening in infancy. PUBLIC HEALTH RELEVANCE: Infants perform worse than adults when listening in noise and we don't know why. The proposed experiment will investigate one mechanism that might contribute to this difference. The results from this experiment will lead to a greater understanding of the mechanisms that contribute to hearing in noise during normal hearing development. Information learned from this research may help to design educational environments with controlled noise levels.